1. Field of the Invention
This invention relates to a PDP (plasma display panel) More particularly the present invention relates to dielectric composition and method for forming the composition, such composition used for mading a dielectric layer or a barrier rib of the PDP.
2. Description of the Prior Art
PDP has been considered the most suitable large size FPD (flat panel display) since the process making the PDP panel is easier than any other FPD.
FIG. 1 shows a structure of the PDP cell arranged in a matrix pattern in the conventional AC type PDP. The PDP discharge cell includes an upper plate having a sustaining electrode pair 12A and 12B, an upper dielectric layer 14 and a protective layer 16 that are sequentially formed on an upper substrate 10, and a lower plate having an address electrode 20, a lower dielectric layer 22, an barrier rib 24 and phospher 26 that are sequentially formed on a lower substrate 30. The upper substrate 10 and the lower substrate 18 are facing each other and a discharge cell is defined by these substrates and the barrier ribs 24. One of the sustain eletrode pair 12A, 12B is also used for a scan eletrode applying scan pulses for scanning the panel. The upper dielectric layer 14 is accumulating an electric charge. The protective lyaer 16 prevents the upper dielectric layer 14 from demaging by sputtering so that it may increase a life of PDP and improve an emission efficiency. Mgo is uaually used for the protective layer 16. The upper and lower substrates 10 and 18 are aligned so that the address eletrode 20 is cross to the sustain electrodes 12A, 12B. Data signals are applied to the address electrode 20 in order to select the cell which is to be displayed. The barrier rib 24 prevents the adjacent cells from leaking ultraviolet rays produced by the electrical discharge. The phosphor is coated on the lower dielectric layer 22 ane the barrier ribs 24 so as to genarate red, green or blue visible ray.
The PDP discharge cell having a structure as described above maintains a discharge by a face discharge between the sustaining electrode pair 12A and 12B after being selected by an opposite discharge between the address electrode 20 and the scanning/sustaining electrode 12A. In the PDP discharge cell, the fluorescent body 26 is radiated by an ultraviolet ray generated during the sustained discharge, thereby emitting a visible light to the outer side of the discharge cell. As a result, the PDP having discharge cells display a picture.
FIG. 2 explains a process of manufacturing the barrier rib 24 shown in FIG. 1 step by step. Referring to FIG. 2, in step S2, parent glass powder and oxide filler powder, which are materials of the barrier rib, are mixed to prepare mixture powder. In this case, fine powder of less than 100 .mu.m is made after the parent glass powder and the oxide filler powder are mixed at a predetermined ration. Next, in step S4, a paste state to be used for the screen printing method or a slurry state to be used for the tape casting method is made by mixing the mixture powder with an organic vehicle. In step S6, by making use of the paste or the slurry, the barrier rib 24 is formed on the lower dielectric layer 22 defined on the lower substrate 18. In this case, the barrier rib 24 is made by the screen printing method, the sand blast method, the etching method, the additive method, the stamping method and so on. This will be described in detail later. Subsequently, in step S8, the barrier rib 24 formed in the step S6 is dried for 15 to 20 minutes at a temperature range of 300.degree. C. to 500.degree. C. to remove the organic vehicle and thereafter is sintered at a temperature range of 550.degree. C. to 600.degree. C., to thereby complete the barrier rib 24.
FIG. 3a to FIG. 3d are sectional views for representing a process of manufacturing the barrier rib making use of the screen printing method. Referring now to FIG. 3a, there is shown a structure in which the lower dielectric layer 22 and the glass paste patterns 28 are disposed on the lower substrate 18. The glass paste patterns 28 are formed by coating a glass paste prepared by mixing the glass powder, which is mixed by the parent glass and the filler, with the organic vehicle on the lower dielectric layer 22 at a desired thickness using the screen printing method and thereafter by drying the same during a desired time. Then, a process of forming the glass paste patterns 28 as mentioned above is repeatedly performed about seven to eight times as shown in FIG. 3b and FIG. 3c. As a result, the glass paste patterns 28 are disposed at a desired height, for example, a height of 150 to 200 .mu.m. The glass paste patterns disposed in this manner are sintered to provide the barrier ribs 24 having a desired height on the lower dielectric layer 22 as shown in FIG. 3d.
FIG. 4a to FIG. 4f are sectional views for representing a process of manufacturing the barrier rib making use of the sand blast method. After a glass paste 30 is coated on the lower dielectric layer 22 formed on the lower substrate 18 as shown in FIG. 4a, a photo resistor 32 is coated on the glass paste 30 as shown in FIG. 4b. Next, as shown in FIG. 4c, mask patterns 34 are positioned on the photo resistor 32 which is exposed to a light through openings of the mask patterns 34 in turn. Subsequently, after the mask patterns 34 are removed, an non-exposed portion of the photo resistor 32 is removed to form photo resistor patterns 32A as shown in FIG. 4D. Then, glass paste patterns 30A are formed in the same shape as the photo resister patterns 32A as shown in FIG. 4E by removing the exposed glass paste 30 through the photo resistor patterns 32A using the sand blast method. Consequently, the barrier ribs 24 are provided on the lower dielectric layer 22 as shown in FIG. 4f by sintering the glass paste patterns 30A after removing the photo resistor patterns 32A.
FIG. 5a to FIG. 5c are sectional views for representing a process of manufacturing the barrier rib making use of the etching method. As shown in FIG. 5a, a paste 34 sensitive to a light is coated on the dielectric layer 22 disposed on the lower substrate 18. Then, as shown in FIG. 5b, mask patterns 36 are positioned on the sensitive paste 34 which is exposed to a light through the mask patterns 36. Consequently, the barrier ribs 24 are made as shown in FIG. 4c by removing the mask patterns 36 and then etching a non-exposed portion of the sensitive paste 34 and thereafter by sintering the non-etched portion of the sensitive paste 34.
FIG. 6a to FIG. 6e are sectional views for representing a process of manufacturing the barrier rib making use of the additive method. As shown in FIG. 6a, a photo resistor 38 is coated on the lower dielectric layer 22 disposed on the lower substrate 18. Then, as shown in FIG. 6b, mask patterns 40 are positioned on the photo resistor 38 which is exposed to a light through the mask patterns 40. Subsequently, the mask patterns 40 are removed and then the exposed portion of the photo resistor 38 is removed to thereby form photo resistor patterns 38A as shown in FIG. 6c. Next, as shown in FIG. 6d, glass pastes 30 are coated between the photo resistor patterns 38A and then dried. Consequently, the barrier ribs 24 are provided on the lower dielectric layer 22 as shown in FIG. 6e by removing the photo resistor patterns 38A and thereafter by sintering the glass paste 30.
FIG. 7a to FIG. 7d are sectional views for representing a process of manufacturing the barrier rib making use of the stamping method. As shown in FIG. 7a, a glass paste 42 is coated on the lower dielectric layer 22 disposed on the lower substrate 18. Then, as shown in FIG. 7b, a mold 44 with holes for the barrier ribs is positioned on the glass paste 42 which is stamped by applying a desired pressure to the mold 44, thereby forming glass paste pattern 42A conforming to the hole shape of the mold 44. Consequently, the mold 44 is separated and then the glass paste patterns 42A are sintered as shown in FIG. 7c to thereby provide the barrier ribs 24 on the lower dielectric layer 22 as shown in FIG. 7d.
The barrier rib 24 which can be made by the above-mentioned various methods serves to increase a brightness of the PDP by reflecting a rear light emitting from the fluorescent body layer 26 along with the lower dielectric layer 22. Accordingly, the lower dielectric layer 22 and the barrier rib 24 requires a dense organization to have a high reflexiblity. Also, the lower dielectric layer 22 and the barrier rib 24 needs a low dielectric factor for improving a response characteristic of the elements, a low expansive coefficient and a thermal stability for preventing a crack, and a low sintering temperature for preventing a crack in the lower substrate 18 at the time of sintering. To this end, a same series of parent glass and oxide filler are used for the lower dielectric layer 22 and the barrier rib 24. For example, as a material of the barrier rib 24 is used a glass-ceramics material in which oxide filler powder consisting of TiO.sub.2 and Al.sub.2 O.sub.3 is mixed with parent glass powder of PbO--B.sub.2 O.sub.3 --ZnO group or PbO--B.sub.2 O.sub.3 --SiO.sub.2 group containing a large amount of Pbo component. More specifically, a composition and a component ratio of the parent glass included in a material of the conventional barrier rib 24 are indicated in the following Table:
TABLE 1 COMPONENT RATIO MATERIAL COMPOSITION (WEIGHT %)
GLASS PbO 60-80 B.sub.2 O.sub.3 10-20 SiO.sub.2 2-10 Al.sub.2 O.sub.3 0.1-4.5 FILLER Al.sub.2 O.sub.3 95-100 TiO.sub.2 0-5 PARENT GLASS (40- 580-600.degree. C. 13-15 70-80 .times. 10.sup.-7 .degree. C. 50-60 70%) + FILLER (30-60%)
wherein the component ratio of the parent glass composition is calculated assuming that a weight of the barrier rib be 100 weight %, and the component ratio of the filler composition also is calculated assuming that a weight of the barrier rib be 100 weight %. As seen from the Table 1, PbO--B.sub.2 O.sub.3 --ZnO group or PbO--B.sub.2 O.sub.3 --SiO.sub.2 group containing the PbO having a large weight of 60 to 80% is used for a parent glass for the conventional barrier rib. TiO.sub.2 in the oxide filler serves to increase the reflective factor and the crystallization of the barrier rib 24. Specifically, since a refractive index of the parent glass proportional to the reflective factor thereof is 1.4 to 1.5 while a refractive index of TiO.sub.2 is 2.7, TiO.sub.2 becomes an important factor increasing the reflexibility of the barrier rib. Also, TiO.sub.2 improves the crystallization of the barrier rib to thereby increase the reflexibility thereof. Meanwhile, Al.sub.2 O.sub.3 in the oxide filler serves to reduce the thermal expansive coefficient of the barrier rib 24. The following Table 2 represents a characteristic of the barrier rib 24 to which a composition having the component ratio as indicated in the Table 1 is applied.
TABLE 2 DIELECTRIC THERMAL SINTERING CONSTANT EXPANSIVE REFLECTIVITY GLASS-CERAMICS TEMPERATURE (1 MHz) COEFFICIENT (400 nm)
However, such a material of the barrier rib 24 has a problem in that, because it has a high dielectric constant equal to 13 to 15, a response speed of the element is delayed. Also, as described above, the barrier rib 24 is formed on the lower substrate 18 and then sintered together with the lower substrate 18. In this case, since the conventional material of the barrier rib 24 has a high sintering temperature, the lower substrate 18 is deformed and damaged at the time of sintering. Furthermore, the conventional material of the barrier rib 24 gives rise to an environment contamination due to PbO occupying a high weight and increases the weight of elements.